No pain no gain.
Embrace the pain.
Embrace the suck.
Suck it up buttercup.
These are things I tell myself on a regular basis. I think every single athlete has points in their training when something similar to the above runs through your mind on a continuous loop. Yes, some days really do suck. Right now nearly every muscle I have is sore. I've been doing pretty well sticking to the training plan, but 8 workouts a week is just exhausting. Some days I want to forget it all and go on a long vacation. A long vacation with sleep, chocolate, and martinis.
Then I have a great run or bike or swim, and realize its all worth it.